Sound-absorbing chamber



March 19, 1929. T. B. MUNROE ET AL SOUND ABSORBING CHAMBEli Filed April6, 1927 2 Sheets-Sheet O 6 j 0 3 nwzb 0 Q 0 March 19, 1929. T. a. MUNROEET AL 1,705,778

SOUND ABS ORBING CHAMBER Filed April 6, 1927 2 Sheets-$heet 2 yZZBJYan/We I flidlace Wafer/ ll r degree.

Patented Mar. 19, 1929;

UNITED STATES PATENT OFFICE.

TREADWAY B. MUNROE AND WALLACE WATERFALL, OF CHICAGO, ILLINOIS; SAIDWATERFALL .ASSIGNOR T0 SAID MUNROE.

SOUND-ABSORBING CHAMBER.

Application filed April 6, 1927. Serial No. 181,590.

This invention relates to receptacles or cells having high soundabsorbing qualities, and has for its object to provide a constructionmore eificient in use than those heretofore proposed.

With these and other objects in view the invention consists in the noveldetails of construction and combinations of parts as will he more fullyhereinafter disclosed and particularly pointed out in the claims.

Referring to the accompanying drawings forming a part of thisspecification, in which like numerals designate like parts in all theviews:

Fig. 1 is a perspective view of a structure made in accordance with thisinvention, and broken away to show the interior construction thereof;

Fig. 2 is a vertical sectional View of the device shown in Fig. 1; 1

Fig. 3 is a partial sectional view, similar to Fig. 2, showing amodified form of construction;

Fig. 4 is a vertical sectional view, similar to Fig. 3, showing a stillfurther modified form of the invention;

Fig. 5 is a'horizontal sectional view taken as on the line 5-5-of Fig.4, and looking in the direction of the arrows;

Fig. 6 is a partial sectional view showing still another modification ofthe invention;

Fi 7 is a view similar to Fig. 6 showing a difi erent arrangement of thebafiies; and

Fig. 8 is a partial perspective view illus trating the construction of apart of the structure as produced by this invention.

In order that this invention may be the more clearly understood it issaid that there are many mechanical devices now in use which createconsiderable noise, the sound of which is objectionable, and it is thepurpose of this invention to provide such an enclosure for said devicesthat the sound emanating therefrom may be absorbed to a high Knowledgeis had of such sound absorptive material as hair felt, etc. but suchmaterial is unsuited for the present purpose chiefly due to itsnon-rigidity.

In Patent No. 1,554,180 issued to W. S. Trader, dated September 15,1925, and entitled Sound absorbing board for walls and ceilings, thereis disclosed a wallboard constructed from Celotex which is a felted massof strong bagasse fibers, so compacted as to be capable of use as anartificial lumber in that it can be sawed and nailed, and has sufficientstrength in many cases to be substituted for lumber. There is alsomentioned in said patent the use of another building board known on themarket as Insulite which is made from wood pulp tailings and whichlikewise has a porous fibrous body portion and which is possessed ofconsiderable strength so that the same can be nailed, etc. The materialCelotex, however, is to be preferred in that it is peculiarly adapted tothe purpose of this invention, because of its cellular construction, orin other words, it has internal cells producing a more or less porousinterior into which sound waves may penetrate with consequent reductionthrough absorption due to heat consuming friction generated on itsinterior by the sound waves traversing its fibrous mass. This fibrousboard, generally indicated by the numeral 1, is provided on one sidewith a great plurality of relatively closely spaced apertures 2 which,however, do not extend completely through the board 1 as clearly shownin the drawings. The ragged irregular surfaces of the apertures 2communicate directly with the open interstices or air cells with whichthe interior of the Celotex board 1 is provided and therefore the soundwaves will readily pass from the walls of said apertures into theinterior cellular casing of the fibrous board, where they penetrate thetangled mass of fibers and strike against the individual fibers in sucha manner as to render impossible their reflection from the board.

The invention more particularly is directed to the construction of areceptacle or sound absorbing cell formed from this perforated Celotexmaterial, as illustrated in Fig. 1, provided with a top 3, a bottom 1,and the necessary plurality of sides 5. Inasmuch as this material hashigh heat-insulating quality, not only is the bottom member 4 providedwith an opening 7 but one of the side Walls such as 8 is also providedwith an opening 9, preferably nearer the top of the receptacle, saidopenings being provided for ventilation. If, for example, the devicewhich creates the obnoxious sound in a motor, indicated by the dashedline 10, it would be necessary to ventilate the enclosing receptacle sothat the heat generated could escape to prevent damage to the motor. Themotor 10 would be mounted upon a base 11 supported above the floor 4 ofthe receptacle as by the standards12, the base 11 being positioned tostraddle the opening 7 in said bottom for a purpose presently to appear.The motor 10 could be connected through its shaft 13 to any suitablemechanism not shown but which could also be included within the sounddeadening chamber.

In order that too high a percentage of the sound waves may not escapefrom the cham her along with the heat created by the device therein, abattle construction is provided-in association with each of the openings7 and 9. Referring more particularly to Figs. 1 and 2, the battle isformed of an auxiliary piece of the Celotex material such as 15, spacedas by the posts 16 from the bottom 4 immediately over the opening 7, butit should be observed that the baffle 15 is of such dimensions that itwill substantially overlap the limits of said opening. The amount ofoverlapping is dependent upon the space provided between the baflie 15and the bottom member 4, the important feature of this relationshipbeing to cause the path of each sound wave to be so broken in escapingfrom the chamber that a high degree of absorption will be obtained.Stated in other words, some of the sound waves from the motor 10 willseek the opening 7, but in so doing they will strike the surfaces of thebottom member 4 and the baffle 15, be reflected from each and absorbedto such an extent by frictional engagement with the rough surfaces ofthe Celotex material that only a relatively small amount of the soundwill leave the chamber.

The side wall such as 8, likewise provided with an opening 9, hassccuredthereto a baffie 20 of the Celotcx material spaced as by the posts 21,and overlapping said opening just as the baffle 15 overlapped itsassociated opening 7 and for the same purpose. In the drawings thearrows indicate the natural air draft through the chamber and are sodrawn to clearly show the tortuous path traversed in entering and leai'ing the chamber.

With reference to Fig. 3 it will be seen that the opening 7 in thebottom 4 has associated therewith a baffle composed of-an upper member25 secured to a lower member 26 both of Celotex material, the apertures2 of which are oppositely directed or in other words are disposed on theexposed surfaces of the baflie. By providing such a construction, alarger percentage of sound absorption is obtained due to the apertures 2of the lower member 26 and the apertures of the bottom 4 facing eachother so that the sound waves, in escaping between said members. will besubjected to a larger absorptive area than was'the case in the singlebafiie 15 discl0sed in Fig. 2 with its unapertured surface opposite theapertured surface of the bottom member.

In Fig. 4 is disclosed a modified form of bafiie construction whereinthe bottom 4 has secured thereto, and extending around the opening 7, awall 30, surrounded by a spaced wall 31 dependently secured to ahorizontally disposed bafile men'ibe'r 32 supported in spaced relationabove the wall 30 as by the supporting posts 33. The members 30, 31 and32 are likewise of lelotex material and the member 31 stops short of thebottom member 4 to permit passage of air waves, but greatly reducedpassage of sound waves thereunder, as clearly shown. Bv such aconstruction the sound waves from within the chamberv are given -a stillmore tortuous path to follow in escaping therefrom and in thisconnection it might be stated that the walls 30 and 31 which are spacedfrom each other are provided on their opposing faces with the apertures2 for sound absorption. F 1g. 5 clearly shows the spacing of the walls30 and'31 as well as the location of the supporting posts 33. which maybe secured to the baffle and bottom members inany suitable manner. I

Tn Figs. 6, 7 and 8 are disclosed a still further modified form of.battle construction wherein the bottom 4 has suitably secured thereto,along two parallel edges of the open ing 7, vertically disposedsupporting walls indicated by the numeral 35 to and between which aresecured a plurality of obliquely disposed baffle members 36 of Celotexmaterial in relatively close spaced relation to each other. In Fig. 6one-half the baffle members 36 are shown inclined in one direction tothe bottom member 4 and the other half of said baflies are shownoppositely inclined to said bottom member, with the two central bafflemembers 37 contacting with each other. Fig. 7 shows all of the battles36 in parallel relation with each other. By this oblique baffleconstruction it will be seen that the sound waves cannot escape from thechamber except after reflection from the surfaces of the Celotexmaterial from which the bafiles are constructed and inasmuch as the saidmaterial is provided with the apertures 2 on one surface thereof thetotal surface area of contact with the sound waves is increased all aswill be readily understood. Further, this construction permits a morerapid rate of ventilation as the air draft is less obstructed. Thedirectional flow of the draft through the chamber may also be controlledin accordance with the nature of the device within the chamber by use ofthe obliquely disposed baffles, 'all as will be readily understood.

It has been found in actual practice that a very high percentage ofsound absorption is attained by the construction as above disclosed.That is to say, in one specific instance of an electric refrigeratingdevice, supplying its own cooling medium, in which the mechanicaloperating unit built into the refrigerator was found obnoxiously noisy,a construction employing the features above disclosed was installed. Inthis particular instance a chamber in accordance with theabovedisclosure was built within the walls 50 and the bottom 51 of therefrigerator, said bottom 51 having therein a ventilating opening 52co-acting with a similar opening in one of the side walls to provide forthe ventilation of the electric motor and pump mechanism supported bythe bottom member 51. In other words, there was installed in thisrefrigerator a construction as disclosed in Fig. 2 of the drawings sothat the opening 7 in the bottom of the sound absorbing chamber was inregistry with the opening 52 in the bottom 51 of said refrigerator, andthe opening 9 of said sound absorbing chamber was in open communicationwith the other ventilating opening in the side wall of saidrefrigerator. Further the power unit of the refrigerating device wasinclosed in the sound absorbing chamber and supported from the bottomfloor 4 thereof so that substantially full effect was had of theapertured surface for absorption of the sound waves, and so that theweight and disposition of said unit would in no way affect the baffleplate 15 associated with the ventilating opening 7. The result was asurprisingly high diminution of noise, the sound absorption beingapproximately Thus it will be seen that by this invention there isproduced a sound absorbing chamber the walls of which comprise buildingboards of fibrous material of a vegetable nature such as bagasse, saidboards having sound absorptive properties due to the porous interiorconstruction thereof, as well as the independent artificial openingsextending inwardly from a surface of the material, whereby sound wavesmay enter said openings and be absorbed by said porous interior. Incombination with such a wall there is provided means to ventilate thechamber which are the openings 7 and 9, as well as means comprising thebaflies which are of the same material as the walls and which coact withthe walls to absorb a high percentage of the sound waves attempting toescape through the ventilating openings along with the air currents.

It is obvious that those skilled in the art may vary the details ofconstruction as well as the arrangements of parts without departing fromthe spirit of the invention and therefore it is not desired to belimited to the above disclosure except as may he demanded by the claims.

VVhatis claimed is:

1. A sound absorbing chamber the walls of which comprise building boardsof fibrous material with sound absorptive properties; positiveventilating means for said chamber including an air inlet and an airoutlet; and

means comprising a cover for one of said air passages said meanscoacting with said walls to absorb a high percentage of the sound wavesattempting to escape through said ventilating means.

2. A sound absorbing chamber the walls of which comprise building boardsof fibrous n'laterial with sound absorptive properties; positivevmtilating means for said chamber including an air inlet and an airoutlet; and means comprising independent members of said wall materialcoa-cting with said air passages and walls to absorb a high percent-ageof the sound waves attempting to escape through said ventilating means.

3. A sound absorbing chamberthe walls of which comprise building boardsof fibrous material with sound absorptive properties; means includingpassages to continuously ventilate said chamber; and means comprising afibrous battle spaced from and coact ing with said passages and walls toabsorb a high percentage of the sound waves accompanying the air throughsaid ventilating means.

4. A sound absorbing chamber the walls of which comprise building boardsof fibrous material with sound absorptive properties; means includingpassages to continuously ventilate said chamber; and means comprising afibrous battle spaced from and coacting with said passages and walls toabsorb a high percentage of the sound waves accompanying the air passingaround each battle and through said ventilating means.

5. A sound absorbing chamber the walls of which comprise building boardsof fibrous material with sound absorptive properties; means comprisingpassages in said walls to continuously ventilate said chamber; and meanscomprising a fibrous baflle having artificial surface openings saidbailie held in spaced relation to a wall and passage and coacting withsaid walls to absorb a high percentage of the sound waves in the airsurrounding said baflle and passing through said ventilating means.

6. A chamber having a Wall provided with openings extending from theinner surface thereof to admit sound waves; an air passage extendingthrough one of said walls; and a cover for said passage likewiseprovided with openings extending inwardly from a surface thereof toadmit sound waves, said cover internally spaced from said wall andcovering only the portions thereof adjacent said passage whereby air inentering and leaving said chamber through said passage is caused to passaround and over said surface of said cover with resultant absorption ofa high percentage of sound waves accompanying said a1r.

7. A chamber having a wall provided with openings extending from theinner surface thereof to admit sound waves; an air passageextendingthrough one of said walls; and a cover for said passagelikewise provided with openings extending inwardly from a surfacethereof to admit sound waves, said Cover internallyspaced from butrigidly secured to said wall and covering only the portions thereofadjacent said passage whereby air in entering and leaving said chamberthrough said passage is caused to pass around and over saidsurface ofsaid cover with resultant absorption of a high percentage of sound acover with resultant absorption of a high percentage of sound wavesaccompanying the air. 9. A chamber having'a wall provided with openingsextendlng from the inner surface thereof to admit sound waves; anair-passage extending throughone of said walls; and a cover for saidpassage comprising parallel obliquely disposed members likewise providedwith openings extending inwardly from a surface thereof tovadmit soundWaves, said cover internally spaced from said wall and covering only theportions thereof adjacent said passage whereby air in entering andleaving said chamber through said passage is caused to pass around andover said surface of said cover with resultant absorption of a highpercentage of sound waves accompanying said air. 7

10. A chamber having a wall provided with openings extending from theinner surface thereof to.admit. sound waves; an air passage extendingthrough one of said walls; and a cover for said passage comprisingparallel members obliquely disposed to the asso ciated wall, saidmembers likewise provided with openings extending inwardly from asurface thereof to admit sound waves, said cover internally spaced fromsaid wall and covering only the portions thereofv adjacent saidpassage'whereby air in entering and leaving said chamber through saidpassage is caused to pass around and over said surface of said coverwith resultant absorption of a high percentage of sound wavesaccompanying said air.

11. A sound absorbing structure having therein a sound producing source,the structure comprising a chamber in which the sound producing sourceis positioned, the chamber having entrance and exit openings whereby acooling medium is circulated into and out of the chamber, means relativeto the cooling medium exit whereby a substantial part of the coolingmedium discharge stream will in escaping at the exit be deflected in itspath of flow, the means causing deflection of the cooling medium streamcomprising a relatively open porous material whereby sound wavesimpacting thereon may pass thereinto to be absorbed and dissipated.

In testimony whereof we affix our signatures.

TREADVVAY B. MUNROE WALLACE WATERFALL.

